Electronic security systems are known in which a resonant circuit is electromagnetically interrogated, the presence of such resonant circuit within a predetermined area under protection being indicative of an alarm condition. Such systems are employed, for example, for pilferage control in retail stores, libraries and the like wherein the resonant circuit is affixed to items being protected, such that unauthorized removal of an item from the protected area will occasion an alarm. A preferred system is the subject of copending application Ser. No. 214,361, filed Dec. 30, 1971, of the same inventor as herein, in which a resonant tag circuit is operative at two frequencies, a first frequency for sensing tag presence and a second frequency for deactivation of the circuit by altering or destroying its resonant properties at the first or detection frequency. Deactivation of the tag circuit is accomplished by applying an electromagnetic field to the circuit of a strength sufficient to fuse a conductive link therein to alter resonant circuit characteristics. The electromagnetic field can be provided by manual actuation when a tag is presented to an attendant for such purpose. It is often desirable, however, to provide an automated means for applying a deactivation field when a tag is presented for such deactivation and also to sense that deactivation has indeed been accomplished.